Etching and fluorination of yttrium oxide (Y2O3) irradiated with fluorine ions or radicals

Surface etching and fluorination of yttria (Y2O3) by energetic fluorine (F) ions and radicals were studied with mass-selected mono-energetic ion beams in an ion energy range of 500-3000 eV and xenon difluoride (XeF2) gas exposure. The etching yields of Y2O3 were evaluated in this energy range and found to be lower than those of silicon dioxide (SiO2). It was also found that, when the ion incident energy was sufficiently low, a small percentage of Y2O3 near its surface was converted to yttrium trifluoride (YF3), rather than yttrium oxyfluoride. However, as the ion incident energy increased, the fraction of yttrium oxyfluoride became dominant and the fractions of Y2O3 and YF3 decreased, indicating that energetic incident F+ ions preferentially removed O atoms and replaced them with F atoms, but also etched YF3 if it formed on the surface. Heating the surface from room temperature to 150 degrees C did not affect the outcome. The results suggest how fluorination takes place on Y2O3-coated plasma-facing surfaces exposed to F-based reactive plasmas in plasma etching systems.